Compensating means for pressure responsive devices



M y 1942- 'J. E. BEVINS 2,283,311

COMPENSATING' MEANS FOR PRESSURE RESPONSIVE DEVICES Filed Feb. 16, 1940 2 Sheets-Sheefl sa 32 as w I DURALUM/A/L/M 3mm.

James L'. Bevi/zs.

y 1942- J. E. BEVINS 2,283,311 COMPENSATING MEANS FOR PRESSURE RESPONSIVE DEVICES Filed Feb. 16, 1940 2 Sheets-Sheet 2- Patented May 19,1942

comrinsa'rnvc MEANS FOR PRESSURE i,- "RESPONSIVEDEVICES James E. Bevins, Wood-Ridge, N. J., assignor to Bendix Aviation Corporation, South Bend, Ind., a corporationof Delaware Application February 16, 1940, Serial No. 319,367

3 Claims.

The present invention relates to pressure responsive devices or indicating instruments, and

more particularlyto altitude and/or temperature compensating means for'such devices or indicating instruments.

The invention is particularly adaptable to pressure responsive devices or indicating instruments of the'type wherein a differential between the pressures acting on opposite sides of a yielding wall of a pressure responsive element such, for example, as a diaphragm, established by a change in one of said pressures, is utilized to operate an indicator or other means in accordance with the rateof change of pressure, and wherein means are provided for the equalization of the two pressureswhen said'change no longer takes place.

An example of an instrument of the type decribed above is a rate of climb indicator for aircraft, and the invention is illustrated and described in connection with such an instrument, but it will be understood that it is not restricted to this particular use.

One of the objects of the invention is to pro- Another object of the invention is to provide a' novel combination of elements constituting means for compensatinga rate of climb indicator for changes in temperature.

A further object is to provide a novel rate of climb indicator comprising a pressure responsive element having a yielding wall subject to a changing atmospheric pressure on one side thereof, flow retarding means for retarding the rate at which pressure on the other side of said yielding wall tends to become equalto said changing atmospheric pressure, and a novel valve structure in which the parts of the valve per se are reation of said valve for controlling and regulating the air flow through said flow retarding means in accordance with changes in temperature,-

whereby said climb indicator is compensated for changes in air density due to'changes in temperature.

Still another object of the invention is to provide, in an instrument of the class described, a

sponsive to changes in temperature to cause opernovel .flow retarding assembly comprising a flowretarding element, and a temperature responsive valve for regulating the air flow through said flow retarding element in accordance with temperature changes.

A further object is to provide a novel flow retarding assembly for an instrument of the class described, comprising a flow-retarding dlfiu'ser element, and a temperature responsive valve for regulating the flow through said difiuser element in accordance'with temperature changes.

A still further object of the invention is to provide a novel flow retarding assembly for an instrument of the class described, requiring no altitude compensation and comprising a diffuser element of porous material of such porosity that the flow of air therethrough is not affected by the difference in air density at difierent altitudes, and a temperature responsive valve for regulating the air flow through said difiuser assembly in accordance with temperature changes to compensate for changes in air density due to tem perature changes. H

Another and important object of the inven-] tion is to provide a novel valve structure having its operating parts of dissimilar metals, whereby said valveis automatically operated in response to changes in temperature.

Yet another object is to provide a novel tem- V said opening, whereby changes in temperature cause relative movement between said valvebody I and said closure member due to different rates of expansion thereof to control said. valve open- 1 ing, and whereby no biasing spring is required for the closure member of said valve. 7

Other objects and advantages of the invention will appear more fully hereinafter from a -con-' sideration of the detailed description which follows, taken together with the accompanying two sheets of drawings. wherein one embodiment of the invention is illustrated by wayof example. Itis to be expressly understood, however, that the drawings are for purposes of illustration and description only, and are not to be construed as defining the limits of the invention, reference being primarily had for this purpose to'theappended claims.

In the drawings, wherein" like reference numerals designate like parts in the several views:

Fig. 1 is a side elevation, partly in section, 0i one embodiment of the invention shown applied to the operating mechanism of a rate of climb indicator for aircraft;

Fig. 2 is an enlarged detail sectional view of the novel flow regulating temperature responsive valve structure embodying the invention, showing its functional relationship to the flow-retarding element;

Fig. 3 is a sectional elevation of a complete rate of climb indicator embodying the invention;

and

Fig. 4 is a partly sectional view of the instru-- ment of Fig. 3, the section-being taken at a different angle to show parts not visible in Fig. 3.

The invention consists substantially in the construction, combination; location and relative arrangement of parts for obtaining the results desired in accordance with the foregoing objects, as will be more fully hereinafter set forth in the specification, as shown in the drawings by way of example, and as finally pointed out in the claims.

Referring now to the drawings, the device embodying the invention, which, in the illustrated embodiment is shown as a rate of climb indicator for aircraft, comprises an operating mechanism mounted, as shown in Figs. 3 and 4, within an instrument casing 5 of any suitable material such as Bakelite, on a frame formed, for example, by a rear frame member or plate 6 and a front face plate I, as shown in Figs. 1 and 2. The plates 6 and I are held in spaced relation in any suitable manner as, for example, by spacing rods 8 and screws 9.

Mounted in the frame thus constituted is a pressure responsive element such as an expansible diaphragm III of any suitable type that is adapted to expand and contract to actuate an indicator or pointer ll through suitable motion transmitting means when a pressure differential is established between the pressure inside of said diaphragm l0 and the pressure surrounding said diaphragm within the casing 5. j

The pressure differential may be established by providing a free passage between the inside of the case 5 and the atmosphere outside of said case, and providing a restricted passage between the inside of the diaphragm and the atmosphere outside of the case; or, as in the illustrated embodiment, by providing a free passage between the inside of the diaphragm l0 and the atmosphere outside of the case 5, and providing a restricted passage, through suitable flow-retarding means, between the inside of said case and the 1 atmosphere outside thereof in a. manner to be described more fully hereinafter.

In the present embodiment, the diaphragm I0 is mounted in a suitablemanner on a flexible arm l2 that is carried by a bracket I3 secured to the rear plate member 6 by means of screws H. Suitable means are provided forv obtaining zero adjustment of the instrument and, as shown in Fig. 1, comprise a set screw l5 having a tapered or coned end It which engages the end I! of the flexible arm l2, said end I! being bent upwardly at an angle to said ar'm l2. The set screw I5 is threaded in a bracket l8 formed aspart of one o the spacing rods 8.

The pressure responsive diaphragm l0 may be attached to said flexible arm I 2 by means of a central boss l9 that extends through said arm l2 to receive a locker washer 20 and nut 2| to securely hold said diaphragm on said arm. The

boss I!) is hollow and connects the inside of the diaphragm ID to the atmosphere outside of the case 5 byrneans of the tube or conduit 22 and through a coupling chamber 23 from which extends another tube or conduit 24 to another coupling member 25 that is vented to the atmosphere outside of the casing through the rear wall of the latter as hereinafter described.

The novel means embodying the invention are now provided for establishing a differential between the pressure inside of the diaphragm l0 and the pressure outside of said diaphragm, i. e. the pressure within the case 5. In the present embodiment said means comprise a flow-retarding element providing restricted communication between the inside and outside of the case for retarding the rate at which the pressure within thecase 5, i. e. the pressure on the outside of the diaphragm l0, tends to become equal to a chang- =rnentioned Patent No. 2,147,962 and carried by a threaded coupling member 21 screwed into a temperature-controlled valve assembly 28 the,

purpose of which will appear more fully hereinafter. To insure. an air-tight fit between the coupling member 21 and the valve assembly 28 a gasket 29 is provided therebetween.

The temperature-controlled valve assembly is located within the casing 5 as shown in Figs. 1 and 4 but is placed in communication with the atmosphere outside of said casing and, for this purpose, is connected to the coupling member 25 by means of a screw 30 which engages the internal screw threads 3| and 320i the coupling member 25 and valve assembly 28, respectively, and which has a central longitudinal, bore 33 therethrough to provide a passage to the interior of said valve assembly from the outside of the casing 5 through the coupling member 25. The coupling member 25 is arranged to be attached to the rear wall 34 of the casing and to provide a further connection to the outside of said casing and for this purpose is provided with ears or lugs 35 engaged by bolts 36 extending through ,the casing. An internally threaded bushing 31 is molded in a boss-38 provided in the rear wall 34 of the casing, and a gasket 39 is provided between said bushing 31 and the coupling member 25 to maintain an air-tight seal therebetween (Fig. 4). Also to provide an airtight seal between the valve assembly 28 and the coupling member 25, one gasket Allis interposed, between said assembly and said couplingmember and another gasket 4| is interposed between the head of the screw 30 and said coupling member 25 (Fig. 1). The valve assembly 28 and the diffuser element 26 project into the casing to a pipe coupling 44 for connecting the inside of the case 5 and the inside of the diaphragm In to a source of static pressure such as the static side of a Pitot tube (not shown) located on an exterior part of the aircraft on which the instrument is carried. i

The diffuser element 26 may be a tube of thin I porous porcelain, although other suitable materials such as carbon, paper, etc., can be used asdisclosed in the aforesaid patent to Rylsky No. 7

-' bly 28 through the coupling me mber i 21 phragm expands until the:aii cpait stopsrdescenq 2,14 .'I?he-difiu s rlelem nt si 195. 1; iro? end-. by. a: cap 14 @and; has vits; o her t n mm: munic'ationwitha passagejfi oi; the valve ss em-,

-- phrqgm wlil Dost, bein T of a -linkr 5 Thus,'by virtue of t e ,fiow eta i g proper) es 7 of the difiusergelement; ZB theinsiQepf the case 5 and, hence, the outside oi -thq diaphrggm is in-r-estrictedgcommunicationwith the sphere outside of said case; through said diiiuse I s H element and through passage l 6,-bqre 33 ,jcoup}ing I ing aij 'niifill ha' I 25, nipp1e,. 43=and pipecouplinglhQnthepthe thez epf and' eixigta'diated hand the inside ofcdiaphragm |v0. is'- in free co n axisoj sei d riock'i'n h it 51 u municationtwith th atmosphereioutside: o contraction 16ft casei through hollow bossjs, tube lg couplin 23, tube;24; Vcoup1ing125; -nipple 13 81;; pipe coup t :jf'ii. 1 1"; j I151: I

Theiront of th ease B isIike ise'Inadeai tight;and, for this purmsethere is provided Should onrrthe ea in a ns zwhiqh eh h the rear, face of the mechanism plate fl the mec anism in 'rinseptedj,thr u ht e.vpe -fxqnfi of the case before sealing the latter. Themecha m'sm-is. h d. se rel in Pl e fi fiin g .1 m? der 4! by means of a split snap ring 48 which a ts the fron -pe i h ral ace q tth a e P ate;- t is-flne l s ale -M 1 9??? s ew 49 urged againstg. sealinghgasket 50 by means of a. split snap i ing 5|, v

From the @foregoing; it will e seen that t inside of the casej;is:air-tightly seaieghand the on1y.c mm mca o 1sthe e om ate-i etbe-o r- 1 thereof is thi'ough theedifi user elen iehtfifi, "and ve 'e m x :2 .-Wh e1t;he p s d .t d ph em ljsinir euqemm n pe on itl'i t .1 mospherewgiit sidepf :thecqse, g ;i es'u 1j t, high Q an ai 'cra ftcga rrying the inst'rngnent: clinibsjt'o hi her altitude, the etmospheric fire in d asesand; cqnse iaen ly t h pr ss, r the diaphragm l0 decreases immediately and co respondinglybecause of-Ithe' iree pa'ss age tothe H atmosphere. The;pissuie'inside theflcfls Eliot].- ever, cannot immediately" equalize withth' .d creEised-j ajtm os phefi'c pressure. .p tside the I becaluse of the restriction prov ided by the d1 iise element 26 end valve'a'ssembly Mind, therefore, i the pressure inside the case 5 is, g "'atei'"'thanj" inside th e diaphragm, therebyicaiisi Q phrag i ,to .cijnti ct lf ntil the iirci ait'stops climb; N ing} 'whefeupoiithe11pie'ss' e ,IinsideftheThese" ernbe 6 n theIi-te'ac 1 ie i e W hf Q id e bs h i t 3 4 .408 and the dia iihragm is restored tonorm'aLjti Inor'de ojcom If the aircraftdes'cends' to la 1o We: zi'ItitIidc, t ev atm0sfpheric p1essui e"increasesg'thereby inime'di I atelyfinc'reasing;the 1p17fss ure inside! fdi J are p'iov'i'ddwhich cbnstitfit p ra' i wh the' pressure out i epf'rth d ovezathe comp n atin phragn i. el'inside the"case'5fcegniiot immed ately; Patent N91 2,147,962 equalize I w1 th the jdecreas'ed I pressure j because of therestricted pa s-age andnhergrdpe; thefdi ingjwhen the pressureswill equalize;

Th expansion and Y contraction 5 'o'fj jthef E d1a phra n is p port a o t r te of chan e o sph r nd ith' rm t the r te. 1 of flow of air between 'theinside' and tside'o'ffl' the casing;S thr ugh difiuSQI 61 merit 25 'and' valvejsgssembly 28;" I i j f,

Motion transmitting means arefnow. p 'oyided I between the: diaphra'g'ni I fand the indicator 50; f pointrl II fo actuati theglatteriin.accord pe I ance with the expansion and contraction" 1;; the air flflows more sl l thrgugh i gfi gf fa id rm wher by, r iidii n ex w l nd c e fth ment; 25 ;-:t1i1e;1eby,cail sing slbwig eque liiatiomm ratejo f im ordesceht o himammed to of the pressure.;.difirgnti1 andvthlis 'producifl 'ff the aw fl he 1mm! hQ X i h l a-v hig ertnd ca onmi;:iat --of ciiinb]oikdescenv drawings said motiontl ahsmittingfineans coin thanis actuall iaki gl g miSe aims? 521 m j i fl ly"im m w 1 5 t n. o an e'fiiit p fie hresent intention-the novel temperature compensating means are so arrangedthat at high temperatures, when the air flows slowly, some or the air which would flow through the ilow retarding element is by-passed through an unrestricted passage, thereby causing quicker equalization of the pressure differential on the diaphragm l8 and at a rate proportional to the changes in density and changes in temperature, and thus preventing a higher reading so that the rate of climb or descent indicated by the pointer II is the true rate. On the other hand, at low temperatures, the by-pass is gradually reduced and finally closed in accordance with the rate of decrease of the temperature, thereby causing more and finally all of the air to flow through the flow-retarding element to produce slower equalization of the pressure differential on the diaphragm l0, and thus preventing a lower" reading so that the pointer II will indicate the true rate of climb or descent.

In the form shown in detail in Fig. 2 of the drawings, said temperature compensating means comprise a springless bi-metallic temperature responsive valve included in the valve assembly 28 which, in accordance with the invention, is made up of two metal castings 11 and 18, the former having the flow-retarding element 28 attached thereto by the coupling member 21 and containing the passage 45 and threaded passage 82. The casting" is hollow, as shown, and is screwed to the casting 11 for ease of assembly and forms a valve chamber I8 having valve opening constituted by a bore 88 in an externally threaded member 8| screwed into the casting l8 and locked by a nut 82.

The chamber 19 communicateswith the passages 46 and 32 by means of a pair of passages 88 and 84 so that air from the casing may flow in freely and without restrictionthrough the valve opening 88 into the valve chamber I8 and out to the atmosphere outside the case 5 through passages 83, 84 and 32, or vice versa.

In order to regulate the flow through valve opening 8|i| as temperature decreases and increases or to completely stop the flow therethrough at a predetermined low temperature a valve closure member is provided which is in the form 01' a relatively short cylinder 85 having a reduced externally threaded portion 88 by which it is screwed into and held rigidly in the metal casting ll, the end of the cylinder 85 being adjacent the inner end of the member 8| so as to completely close the opening 88 at a predetermined temperature.

Relative movement between the valve opening 88 and the valve closure member 85 is obtained in accordance with changes in temperature by making the casing 18 of one kind of metal as, for example, Duralumin, and making the valve closure member 85 or another kind of metal such as Invar, for example, thus providing a springless bi-metallic valve which is per se responsive to changes in temperature.

is not limited thereto'and is capable of a variety valve opening 80 is completely open at about 25 C, and becomes completely closed at substantially -30 C. Thus, the flow of air through the valve opening is regulated in accordance with changes in temperature to compensate for errors due to changes in density, which are accompanied by such temperature changes.

If desired, for convenience in making the zero adjustment of the pointer II by means of the set screw l5, the latter may be arranged for actuation from outside of the case 5 by suitable means such as shown in Fig. 3 of the drawings, wherein the setscrew l5 carries a gear 81 meshing with a pinion 88 secured to or formed integrally with an operating shaft 89 journaled in auxiliary compartment 88 of the casing 5 with one end of said shaft extending out of the case, said outer end being provided with a knurled knob 8| for manuallyrotating the shaft. By turning the knob 8|, the diaphragm l0 may be moved bodily up or down by the spring arm I! as viewed in Fig. 3, thereby adjusting the pointer to zero through the motion transmitting mechanism.

There isthus provided a novel construction of a rate of climb device embodying noveltemperature compensating means in the form of a springless bi-metallic valve which is per se temperature responsive, requiring no bi-metal strips or spring-biased movable valve parts, and which may be capable of use for other purposes than for main a rate of climb device.

While only one embodiment of the invention has been illustrated and described by way oiexample, it is to be understood that the invention oi physical embodiments which will now appear to those skilled in the art to'which the invention appertains, and that changes may be made in the form, details of construction, and arrangement oi the parts and in the materials used, without departing from the spirit or scope of the invention. Reference is, therefore, to be had to the appended claims for a definition of the limits said case for controlling the retardation of the Since the expansion and contraction of Duralumin is much greater than of Invar, it will be seen that at low temperatures the member 8| and itsopening 88 will move toward the closure .member 85, and at high temperatures member 8| will move away from flow of air between the inside'and outside of said case when the atmosphere pressure changes, said assembly consisting of a valve body providing a valve chamber having. a valve opening leading into the inside ofsaid case for direct but controllable passage of air between the inside of the case and the atmosphere outside of said case, a valve closure member rigidly mounted in said valve chamber for cooperation .with said valve opening, a single porous diffuser element mounted on said valve body in parallel air flow relation with said valve opening and providing flow-re stricting passage between the inside and outside of said case, said valve body being of duraluminum and said closure member being of invar, whereby said valve body expands and contracts to a greater extent than said closure member in response to changes in temperature, to produce relative movement therebetween for regulating the flow of air through said valve opening for direct communication with the atmosphere outside of the case and causing more air to flow through said difiuser element at low temperatures than at high temperatures to compensate for errors due to the diiference iii viscosityof the air at different temperatures, and means for iYli' tially adjusting the relative distance between said valve opening/and said valve closure member for calibration purposes.

2. In a rate of climb indicator, a substantially air-tight case, a pressure responsive expansible diaphragm within said case having the inside thereof irrfree communication with the atmosphere outside of said case, indicating means including a pointer, motion transmission means connecting said pointer to said diaphragm for actuation thereby, and a now retardingassembly closure member being of different materials having different temperature coeffici'ents of expansion and contraction, whereby relative movement of said valve closure member'takes place in response to changes in temperature to regulate the I flow of air through said valve opening for direct communication with the atmosphere outside of the case, thereby regulating the amount of air flowing through said diffuser element in accordance with said changes in temperature to compensate for errors due to changes in viscosity of the air caused by said temperature changes.

3. In a rate of climb indicator, a substantially air-tight case, a pressure responsive element within said case in communication with the atmosphere outside of said case, indicating means,

' motion transmission means connecting said indi mounted in said case for controlling the passage the atmosphere outside thereof and consisting of" eating means to said pressure responsive element for actuation thereby, and a flow retarding assembly mounted in said case for controlling the passage of air between the inside of said case and a single flow retarding element providing restricted communication between the inside and, outside of said case, and a springless bi-metallio valve responsive to changes in temperature in by-pass relation to said retarding element for defining direct communication between the interior of said case and the atmosphere exterior thereofand for regulating the amount of airflowing into and out of said case through said retarding element.

JAMES E. BE VINS. 

